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  1. #1

    Question Budget A/C System... Anybody try this?

    I'm doing a budget A/C install on my house (1600 S.F) since money is tight and figure it's an excuse to play around a bit.

    That being said, Heres what I have:

    Take out: 5 ton 10 SEER AMANA unit which wil have a new 4 ton Copeland Scroll installed as well as an 825 RPM C.F.M

    I'm thinking a 75,000 BTUH furnace with either a 4 ton 13 seer evap or 5 ton 10 seer evap with TXV depending on what I come across. My hopes is that even though it is an older unit it will still be reasonably efficient given the larger condensor size and large evaporator to match.

    Has anyone tried something similar to this and if so how did it work out? Any thoughts on this?

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,358
    Sounds like you're trying to engineer a system on a paper napkin.

    Money may be tight...but you may end up spending a lot more thinking you're saving a little.

    If you're in the trade and don't mind nursing along your own frankensystem, you should already know it may not be a smooth watch.

  3. #3
    Join Date
    Jul 2005
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    5,576
    On a simple straight A/C system it isn't rocket science. A TXV eliminates a lot of issues. BTW, yes I have done exactly what you described. Different size, different brands, but same thing.
    Last edited by hvacrmedic; 03-18-2008 at 01:08 AM.

  4. #4
    Join Date
    Mar 2005
    Location
    Houston, Texas
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    11,874
    Quote Originally Posted by The Tucson Tech View Post
    I'm doing a budget A/C install on my house (1600 S.F) since money is tight and figure it's an excuse to play around a bit.

    That being said, Heres what I have:

    Take out: 5 ton 10 SEER AMANA unit which wil have a new 4 ton Copeland Scroll installed as well as an 825 RPM C.F.M

    I'm thinking a 75,000 BTUH furnace with either a 4 ton 13 seer evap or 5 ton 10 seer evap with TXV depending on what I come across. My hopes is that even though it is an older unit it will still be reasonably efficient given the larger condensor size and large evaporator to match.

    Has anyone tried something similar to this and if so how did it work out? Any thoughts on this?
    Sounds like a lot of home owner questions to me.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,367
    Sounds like a lot of guess work. Not enough thought to why.

    You want to build this for your house ok. I can understand the financial reasoning, and the desire to tinker.

    When you sell this house, are you going to put a matched system in, so the new owner doesn't have a play thing for heating cooling system.

    Why are you slowing the blower, how did you determine the proper CFM air flow for the OD unit.
    Are you going to check capacity when its in an running.
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  6. #6
    Quote Originally Posted by beenthere View Post
    Sounds like a lot of guess work. Not enough thought to why.

    You want to build this for your house ok. I can understand the financial reasoning, and the desire to tinker.

    When you sell this house, are you going to put a matched system in, so the new owner doesn't have a play thing for heating cooling system.

    Why are you slowing the blower, how did you determine the proper CFM air flow for the OD unit.
    Are you going to check capacity when its in an running.
    The surface area of the condensor on this unit is roughly 34 sq ft. as a two pass design. A 13 SEER 4 ton Rheem or York System has approximately 23 Sq ft of 1 pass condensor surface. Both York and Rheem are running at about 3500 CFM for the same unit. I will match these CFM numbers within reason by matching the fan blade and motor RPM accordingly.

    To say that this system will be a burden on a future homeowner is not a really a fair judgement. It's a numbers game, not a mystery. I just want to make sure I have my basis covered and am not overlooking anything, thus my reason for posting on here.

  7. #7
    Join Date
    Jun 2007
    Location
    Round Rock
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    3,587
    Everything sounds a bit oversized to me. But its your house. If you're a homeowner and not in the biz. Good luck. I would do something else. It may or may not work, who knows. If you're in the biz, then you know the answers to the questions. If I need something, I get it at cost. I usually look for damaged or returned stuff. I personally wouldn't do the frankensystem. My boss put a 2 1/2 ton scroll in a 5 ton body for craps and grins about 2 years ago. It made it a summer and it still runs, he just didn't like the way it did, he had to overcharge it to get it to cool. Needless to say, he spent the money and did it right about a month ago.

  8. #8
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    Jul 2005
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    Quote Originally Posted by bmathews View Post
    Everything sounds a bit oversized to me. But its your house. If you're a homeowner and not in the biz. Good luck. I would do something else. It may or may not work, who knows. If you're in the biz, then you know the answers to the questions. If I need something, I get it at cost. I usually look for damaged or returned stuff. I personally wouldn't do the frankensystem. My boss put a 2 1/2 ton scroll in a 5 ton body for craps and grins about 2 years ago. It made it a summer and it still runs, he just didn't like the way it did, he had to overcharge it to get it to cool. Needless to say, he spent the money and did it right about a month ago.
    I don't think you can blame the not cooling problem on the larger coil. Maybe he didn't upsize the piston or install a TXV?

  9. #9
    Join Date
    Jan 2004
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    Lancaster PA
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    You wouldn't upsize the piston when installing a 2.5 ton compressor in a 5 ton condenser.



    To the OP.
    Its more then a numbers game if you seel the house with this thing still installed.
    When a service tech comes out and sees the mismatch.
    First thing he'll say to the new HO, is you got a f-ed up system.
    makes you look bad.


    Projects like this can be good learning labs. But should never be left for someone else later down the road.

    Getting your air flow over the OD coil, will still be a lot of guess work. A double row coil has higher resistance then the single rows.Fan blade selection will take a couple guesses.
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  10. #10
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    Jul 2005
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    Quote Originally Posted by beenthere View Post
    You wouldn't upsize the piston when installing a 2.5 ton compressor in a 5 ton condenser.
    If it originally had a 2.5 ton evap coil with piston, then yes, you'd have to upsize the piston or install a TXV. I believe this has been covered, but Carrier sent us instructions for upsizing the piston (a piston resizing chart) for 13/10 SEER mismatches.

    The only difference between the 10SEER condenser and the 13SEER condenser in the base models is the coil size and compressor size. I suppose Carrier knew people might sell the house with those Frankenstein systems on them, but with Carrier's blessing I suppose that makes it a different thing altogether than what this guy is wanting to do.

    Here's my TCW, the only difference will be that he won't have any performance data for some future tech to reference. I've seen a lot worse than this on homes that people buy. Although, it could prove embarrassing for the tech who did it if the next tech who comes out to work on it has the opinion that it can't work, whether or not it actually does.

    I've seen many and various sorts of modifications made to resi systems over the years. Some are pure genious, some reflect a good idea that simply wasn't carried through correctly, and some are just plain hack jobs that cause lost efficiency and/or capacity amongst other serious issues. I judge each modification based upon its merit and not by its political correctness

  11. #11
    Join Date
    Jan 2004
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    I was refering to the 2,5 ton compressor in a 5 ton evap.
    You wouldn't use a 5 ton piston on the evap..
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  12. #12
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    Mar 2005
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    Houston, Texas
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    Possibly by the time this beast is assembled ,T T T (The Tuscon Tech) will have enough posts to get in the Pro sections. It would be interesting to see what this creation does. Keep us posted.

  13. #13
    I stand by my original statement, there's no magic here. It's a numbers game, short and simple. System pressures are key items for system design. I've done my homework on this and coil sizing and airflow will be adjusted to set proper pressures. With that being said, if you have good pressures and a proper split whats left? I would like to think that any good tech would know how to identify a system similar to this and service it accordingly without selling the customer a new system based on the attitude of " I don't understand how it could work, it must not." I'm not sure that this unit will be in place when I sell the house, I do however think that there are a few people on this board smart enough in this trade who understand the fundamentals enough to be completely content with this system if they came across it.

    I will be sure to post my results with this system in the weeks to follow. Hopefully in the "Pro Section". I still need to round up a furnace and coil however and with the weather bouncing around I will probably slack a bit on the install rush... ; ) I'll keep ya guys posted...

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